Subject: Re: A New Night Species
Date: Jun 28 10:36:10 1997
From: Christopher Hill - cehill at u.washington.edu


On Fri, 27 Jun 1997, Michael Price wrote:

> Hi Tweets
>
> Oh, the joys of insomnia.

[snip]
> New species for the night watches last night, though: Caspian Terns going
> over south to north at 3:50 AM PDT, full dark what with the overcast.
> Daytime they're routine, flying in groups overhead whenever the rising tide
> pushes them off the sandbars of Spanish Banks, and my house is on the route
> they take back over Point Grey to Iona Island or Roberts Bank, wherever.
>
> They spend a lot of time loafing around on tidal sand- and mudflats in
> Vancouver BC, all adult birds. So I'm curious about what they're actually
> doing here if their nearest nesting colonies are a hundred or more miles to
> the south. I've not heard of them being nocturnal, and last night's
> occurrence being a personal first (and they wouldn't be hard to hear if they
> habitually travel at night-- sounded like a bunch of rowdy drunks rolling
> home from a late party, all idiotic yee-ha and hoarse rebel yells: Yow!
> Yeah, Yowza!). So, do they feed and loaf during the day and fly the hundred
> or two miles to feed their young at night? Or why so many (sometimes over
> 250-300 adults at the Roberts Bank Jetty) local adults and no local
> breeding? That doesn't make a lot of sense; in nature, no adult animal
> willingly undertakes vows of chastity.
>
> Cheers
>
> Michael Price When I found out that seven of my years
> Vancouver BC Canada was only one of theirs,
> mprice at mindlink.net I started biting absolutely everything.
> -Max Carlson (Ron Carlson's dog)
>
>

A couple of thoughts:

1) At our house in Everett, WA, Caspian Terns are a regular flyover at
*any* hour. "Tern O'clock" my wife will mumble, roll over and go back to
sleep. So I think that it's fairly routine for them to be about at that
hour, and probably doesn't reflect a long distance nocturnal commute. I
don't know what the Caspians are doing in the wee hours, though. I've
spent a night in a large Common/Roseate tern colony and things got very
quiet after nightfall. I don't think that any of the breeding Commons and
Roseates were out foraging.

2) It's been a couple years since Caspian Terns actually bred in Everett,
but they're still hanging around in fair numbers. Around all tern
colonies that I've visited (half a dozen), there has been a contingent of
non breeders hanging around amounting to maybe 10% of the total birds
present. Many of the non-breeders are in full adult plumage. I think with
birds like Caspian Terns, who may live 20+ years, it's not abberrant for
adults to take a year off breeding because something doesn't work out -
maybe the spot they used to nest in has been made unsuitable, and they
take a breeding season or two to find a new spot that will work. Or maybe
a certain proportion of adults are not it tip top condition and just forgo
breeding for a year. When you live as long as a tern, it may be a better
strategy to wait for next year than to take a chance on an iffy attempt
this year.

Chris Hill
Everett, WA
cehill at u.washington.edu